He has decorated it with anti-government drawings, religious pictures and satirical caricatures of Mikheil Saakashvili, the Georgian president.

However, despite the bars on the door and window, this is not a prison - it is actually a television studio, where the country's most unusual political talk show, Cell No. 5, is filmed.

Gachechiladze, who performs under the name Utsnobi - The Unknown - and is the brother of a prominent opposition leader, says he will remain in his self-imposed incarceration until President Saakashvili resigns.

"He describes himself to the West as a democrat, although I think even the West doesn't believe him any more."

"Any normal person knew that war with Russia would be terrible, so Saakashvili has to face... what he did"

Merab Chikashvili, political activist

Cell No. 5 was launched amid the build-up to mass protests outside the Georgian parliament this week, as a coalition of opposition parties attempts to force Saakashvili to step down.

Opposition supporters blame him for leading Georgia to a humiliating defeat in the war with Russia last year, leaving hundreds dead and damaging the fragile economy of this small former Soviet republic.

In a scruffy office in central Tbilisi, a group of student activists is trying to think up new ways to publicly ridicule their president.

The students are responsible for covering the walls of the capital with provocative posters which feature unflattering photographs of Saakashvili and a one-word slogan: Why?

"When he came to power, a lot of people were hoping for change and they trusted him blindly, but although he started in a democratic way, he became much more dictatorial," says Merab Chikashvili, one of the group's leaders.

Democracy pledge

Saakashvili was swept to power following the "rose revolution" in 2003, promising to create a more prosperous, European-style democracy and win membership of Nato.

His supporters say he has cracked down on corruption and attracted much-needed foreign investment.

But his opponents claim that he has held on to power by falsifying elections and stifling freedom of the media, and that he lost Georgian territory during the fighting with Russia.

"Any normal person knew that war with Russia would be terrible, so Saakashvili has to face the responsibility for what he did," says activist Merab Chikashvili.

Some government ministers have suggested that the opposition is effectively doing the Kremlin's work by stirring up political unrest and trying to oust their pro-Western leader.

The president's supporters have also expressed concerns that the demonstrations could turn violent, raising fears of a return to the political turmoil of the early 1990s, when newly independent Georgia collapsed into civil war.

"This country has a very negative experience of radicalisation," says David Bakradze, the chairman of the Georgian parliament and a close ally of Saakashvili.

"If we again turn back into chaos and disorder, it will not benefit the opposition, the government, or Georgia as a country."

The Georgian interior ministry has released police surveillance videos of opposition supporters allegedly buying weapons as part of a plot to stage an armed uprising.

But the opposition insists that the secretly recorded tapes were propaganda tools, intended to "intimidate the public in order to stop them taking part in the rallies," according to one opposition leader, Irakli Alasania.

Alasania has warned the government against using force to disperse the protesters, saying it would be "disastrous for the country".

In 2007, President Saakashvili ordered riot police with rubber bullets, tear gas and water cannon to break up demonstrations, damaging his international image as a progressive reformer.

The authorities have warned that this week's protests must remain within the law.

"Demonstrations and rallies are part of any normal democracy, but if there is any unlawful action like storming government buildings, obviously this is a case when the state is authorised to intervene to maintain basic law and order," says parliamentary chairman David Bakradze.

Rising political tensions

Renewed instability could hit Georgia financially, an international credit-rating agency has predicted.

"Rising domestic political tensions risk making it more difficult for the Georgian authorities to bolster confidence and rebalance the economy following the shocks of the 2008 war with Russia and the global financial crisis," the Fitch agency said in a statement.

The government has offered dialogue and political concessions in an attempt to avoid a showdown, but the opposition has rejected the offer as a sham, and called on Saakashvili's allies in the United States and Europe not to intervene to protect him.

"The protests will continue until Saakashvili goes," says Nino Burjanadze, who helped to lead the "rose revolution" but formed her own opposition party last year. She is one of several former high-ranking officials who have defected and become outspoken critics of the administration which they once served.

As political tensions escalate, some people have expressed hopes that the highly-respected Patriarch Ilia II, the head of the Georgian Orthodox Church, will intervene to avert confrontation on the streets of Tbilisi.

In Giorgi Gachechiladze's television-studio "prison cell", a candle burns next to a religious icon. But, the singer insists, any compromise with President Saakashvili is unthinkable.

"These protests will be like an avalanche or a tsunami," he says. "They can't be stopped."